Within core and metropolitan optical networks, data are transmitted by optical signals aligned on regular grids of optical frequencies with regular channel spaces equal to 400 GHz, 200 GHz, 100 GHz or 50 GHz standardized by the international Telecommunication Union (ITU). The shortest channel spaces correspond to the higher spectral efficiencies and therefore make it possible to transport more capacity. Those channels spaces also correspond to the most detrimental physical degradations such as non-linear impairments during propagation along the optical fibers. Filtering and isolation issues also cause degradation of the optical signals in transparent optical network nodes. The grid standardization is convenient for the optical transparency because it makes it easier to transfer optical signals from network link to network link across the optical nodes in a transparent manner without costly conversion in the electronic domain.
The recent advent of coherent detection for high data rate transmission combined with the availability of bandwidth-agile Wavelength Selective Switches raised the interest for optical transmissions with non-standard channel spacing.
US2006/251419 describes a method to allocate bandwidth from a first node to a second node in a optical network of nodes coupled by optical links. The method begins by accepting a request from an end-user, who requests a virtual path between the first node and the second node. The virtual path has a bandwidth requirement associated therewith. A physical path between the first and the second nodes is selected from a number of such physical paths. The service provider then determines whether the physical path has enough available bandwidth to meet the bandwidth requirement of the requested virtual path. The steps of selecting a physical path and determining the available bandwidth for the physical path are repeated until either an acceptable physical path is found, or every one of the plurality of physical paths has been selected. If an acceptable physical path is found, the acceptable physical path is allocated.
GB2329291 describes a wavelength division multiplexing optical fiber subscriber network capable of expanding the number of subscribers. An allocation of bandwidth method for requested services is carried out in a central office of the optical fiber subscriber network. If a service request signal is received, an exchange controller determines the available remaining bandwidth of each optical wavelength of a subscriber group, from the first optical wavelength towards the last optical wavelength. It determines whether the detected remaining bandwidth on each wavelength is wider than or equal to the service requested bandwidth, until a wavelength with sufficient remaining bandwidth is identified. When the available bandwidth for any one of the subscriber optical wavelengths is equal to or wider than the requested service bandwidth, the controller of the exchange allocates the requested bandwidth to provide the requested service to the requesting subscriber.
US2003/072052 describes an optical wavelength distribution method to allocate wavelength in a network in order to optimize non-blocking traffic throughput to a core network. The network provides network end-to-end transport based upon the allocation of optical carriers of specific wavelengths and implements the distribution of the appropriate optical carriers to achieve the required end-to-end wavelength path connection across the network.